Pavement markers have become widely accepted as permanent installations for providing visible signals which mark traffic lanes and control the flow of traffic on roadways in combination with, or in place of, conventional painted traffic lines. A large number of such markers employ retroreflectors which retroreflect light emanating from oncoming vehicles to provide a signal visible to the operators of such oncoming vehicles.
Reflective pavement markers are designed to withstand high impact forces expected to be encountered on the highway. One of the earlier types of markers of the style generally still used today is shown in the Heenan U.S. Pat. No. 3,332,327. In the basic structure shown in the '327 patent, the plastic retroreflectcr elements are first formed as part of the walls of a hollow shell, and then a layer of metal, by vacuum metallization, is deposited on the cube corner retroreflector elements. Following that step, the "shell" is filled or "potted" with a rigid epoxy-type material. The resulting structure is relatively rigid and over the years has proven to be remarkably durable in use.
In spite of the success of road markers utilizing the potted shell design, the potting material is relatively brittle and can prematurely crack from repeated vehicular impacts. Cracking of the interior fill weakens the marker and, upon further impacts, may cause partial or complete fracture in the external shell, dislodging of the marker from the pavement, and partial loss of retroreflectivity of the lens due to separation of the potting material and reflective coating from the cube corners. This phenomenon can be more pronounced when the marker is secured to uneven pavement.
It is an object of the present invention to provide a potted shell type retroreflective pavement marker which has increased resistance to impact damage.
It is another object of the present invention to provide an improved potted shell type retroreflective pavement marker which has increased useful life.
It is yet another object of the present invention to provide a potted shell type retroreflective pavement marker which is less susceptible to deterioration when secured to an uneven pavement surface.
Other and further objects of the invention are apparent from the following discussion of the invention and the preferred embodiments.